An electric vehicle (EV) charging system may basically be defined as a system for charging a high-voltage battery mounted on an EV by using power of an energy storage device or a power grid of a commercial power source. Such an EV charging system may have various forms according to a type of EV. For example, the EV charging system may be classified into a conductive type using a charging cable and a non-contact wireless power transfer (WPT) type (also referred to as an ‘inductive type’).
When charging the EV, a vehicle assembly (VA) (i.e., a reception pad in the VA) mounted on the EV makes an inductive resonance coupling with a transmission pad of the a ground assembly (GA) located in a charging station or a charging spot, and charges the battery in the EV using power transferred from the GA through the inductive resonance coupling.
The WPT system of the inductive type is a system that transmits electric power using a mutual electromagnetic induction phenomenon between the transmission pad (i.e., a transmission coil) and the reception pad (i.e., a reception coil). Accordingly, when there is a foreign object such as metallic or magnetic material between the transmission coil and the reception coil that can affect the magnetic field, the foreign object directly affects the resonant frequency of the WPT system, resulting in abnormal operation of the WPT system or decrease in efficiency of the WPT system. Also, temperature of the foreign object between the transmission coil and the reception coil may increase rapidly so that stability of the WPT system may be blighted. Therefore, a method for detecting a foreign object between a transmission coil and a reception coil is demanded.